Author(s)

Carra L. Schriber, Mark E. Venable^*

Biology Department, Appalachian State University, Boone, NC, USA.

The induction of biofilm formation has been explored as a means of harvesting microalgae for bioprocessing applications. Environmental stressors have been implicated in the induction of biofilm formation; however, it is unclear whether all stressors, or a select few, are responsible. This study aimed to investigate the effects of three stressors, nitrogen depletion, reduced or elongated day lengths, and increased culture turbulence on bio-film formation of Parachlorella kessleri. We also examined corresponding effects on growth and production of reactive oxygen species. Turbulence induced the greatest response in which a significant decrease in growth plus an increase in superoxide production and flocculation efficiency were seen for the 300-rpm treatment. For varying day lengths, stress response was not observed, however, a significant increase in EPS secretion was measured in both shorter and longer days. Nitrogen depletion induced a low-level stress response, in which superoxide production increased for the highest concentrations, while growth was not impacted. In contrast to previous studies on nitrogen depletion, a significant increase in EPS secretion was not observed. Results indicate that stress response varies according to type and magnitude. EPS production and thus biofilm formation are not linked to the stress indicators investigated. P. kessleri uses small quantities of EPS to contribute to cell stickiness, but not necessarily to the full formation of a biofilm; however, cell stickiness served as a mechanism for substrate adherence and cellular aggregation none the less.

Parachlorella kessleri, Algal Physiology, Biofilms, Day Length, Microalgae, Nitrogen Deficiency, Turbulence

Schriber, C. and Venable, M. (2019) The Effects of Environmental Stressors on Aggregation in Parachlorella kessleri. Journal of Environmental Protection, 10, 1657-1676. doi: 10.4236/jep.2019.1012099.